Variations in FLT3 expression level have relatively little impact on in vitro sensitivity to the cytotoxic effects of FLT3 inhibitors. (A) Scatter plot showing FLT3 mRNA expression levels of cryopreserved MNCs from 64 patients measured by a real-time PCR method relative to expression of the housekeeping gene S14. Cases are grouped according to FLT3 mutation status. Analysis by the Student t test showed no significant differences in FLT3 RNA expression between mutation groups. (B) Mean MTS-derived cytotoxic dose responses of cells from 43 patients to lestaurtinib and PKC412. Cases are grouped by FLT3 mRNA expression level relative to the population median. Error bars represent the SEM. P values refer to a comparison of high and low FLT3 expression groups at each dose using the Student t test (only significant P values [P < .05] shown).